Carburator tuning.

[Firebird!]

Here is me again with carb tuning.
Got a fresh rebuilt engine and rebuild carbs.
Got engine broken in and adjusting carbs now.
In general I am satisfied how engine works. I think I had some hesitation at the beginning of the throttle - rpms were rising slowly and then jumped from about 4500 to 5000. Changing pop-off from 50psi to 30psi seemed to fixed it.

Ok, back to the topic. Trying to do it by the book, starting with idle. I was able to find that sweet spot adjusting Low Speed adjusters, watching my digital tachometer, to the point where little more or little less would screw up the rpms. That worked for the 1st(mag) and 2nd(center) carbs. For the 3rd(PTO) I couldn't get it. I did see some changes in rpms when I went to almost closed or way open. Also 1st and 2nd cyclinders felt quite warm during idle when the 3rd was pretty much cold. Also when inspecting the plugs - the 1st and 2nd were dry, the 3rd is wet. The pics were taken after about 5 min of idling.

What am I missing here?

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[butterbean_29512]

Re: Carburator tuning.

Unless you have a highly modified motor, and I do mean HIGHLY modded, it is best to stick to what the manufacturer set the carbs to at the factory. Exception being the GP1200R, there is a jetting solution that works great for them. What model ski do you have? Once we know the model, you can get much more help.

[Firebird!]

Re: Carburator tuning.

It's Yamaha SUV. With 65U non-pv motor. Nothing highly modified, just K&N FA and oil pump removed. I'm leaning towards the ignition coil being bad for that cylinder, which I'm going to check next. Just wanna see what you guys are thinking.

Unless you have a highly modified motor, and I do mean HIGHLY modded, it is best to stick to what the manufacturer set the carbs to at the factory. Exception being the GP1200R, there is a jetting solution that works great for them. What model ski do you have? Once we know the model, you can get much more help.

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[driftmaster]

Re: Carburator tuning.

Check for play in your throttle shafts. 55psi is the best pop off if your run am flame aresters.
Outside bill carb up date is a must imo. Always genuine Mikuni parts. Get T handle adjustment screws. Check the fuel pump check valves probably have a creased one or two. I've creased them first time out just like bill says. I'm very hard on the 65u I run and been trying to get cards tuned perfectly for the last 4 years.
I put in new needle and seat a couple two three years ago and I'm installing new genuine mikunis again this week. I also have a new intake manifold that's going to allow me to turn the carburetors 45° so I can link shafts. It will help keep from wearing the shaft bushings out so quickly.

I wouldn't have taken off the variable speed oil pump they save tremendous amounts of oil if you do much mid low range RPM time

[Firebird!]

Re: Carburator tuning.

Ok, I got checked the spark with the spark gap tester. I observed the spark at all three cylinders but it seemed that specially at third (PTO) it was intermittent.

So I built the peak voltage adapter and checked the output peak voltage of CDI unit. It was below the spec. around 70v.

Then I checked the Charge coil peak voltage. Below the spec. - around the 70v again.

While I was there checked the pulse coil voltages got 2v, 3v, 4v. (below, right on, above)

But resistance of all coils is within the spec.

Is it possible? Does it still mean that I have a problem there?

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[Firebird!]

Re: Carburator tuning.

Ok, replaced the charge coil and pulser coils from the used unit I got from eBay. Measured over 110v on a charge coil now (was about 70v). Checked the sparks with spark gap tester. The sparks now beautiful: brigher and consistent on all cyclinders. What a change!

Still have 2, 3 and 4volts on pulser coils, don't know why that difference - but since I see sparks - it is probably still working.

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[Firebird!]

Re: Carburator tuning.

Ok, changed all my low speed jets to 100. N/S 1.5 with 115g springs - pop off gauge showed 50 psi for all carbs. No drips at idle.

Found a sweet spot that gives highest rpms at idle with low speed adjusters. The plugs look good at that setting. But also at that setting when I open the throttle - engine dies. Have to 'baby it up' to the high rpms.

I opened the low speed adjusters - of course the rpms dropped - had to bring it back up with idle screw - and of course the plugs look wet now, but the hesitation went away and now the engine doesn't die when I open a throttle.

Does it meant that my pop-off too high or low speed jets are too low?

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[whazguude]

Re: Carburator tuning.

Tacos! Fish tacos. Um.... You know Mikuni makes a book about this, right?

[Firebird!]

Re: Carburator tuning.

Not everybody is as good as you - may be you being such a genius can point me out in that book where it says how to fix this condition?

Tacos! Fish tacos. Um.... You know Mikuni makes a book about this, right?

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[Grumpy Old Guy]

Re: Carburator tuning.

Should have left it stock. LOL

[driftmaster]

Re: Carburator tuning.

Can't remember if you did the balance mod or not, anyway 105 low jets are what you should have. I found with 100 lows it didn't want to come back to idle like it should, real close a lean hang. I'm thinking going to 107.5 or 110 to be able to screw the low in a bit. Feel like I'm still rich at idle. Normally you can just lower the pop off to compensate or double check that your jetting is correct. I do still think 43 psi pop off is the best for the 65u but your going to have dribble. I do to much idling to have dribble.

The 65u I'm running does have port work and may be the reason for me needing the 107 or higher lows.

[whazguude]

Re: Carburator tuning.

Not everybody is as good as you - may be you being such a genius can point me out in that book where it says how to fix this condition?

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You want to pay me to fix it for you???? As Grumpy said, you should have left it stock. Why the fuk you fuk with sh!t you have no clue about........ Some people's children.

[whazguude]

Re: Carburator tuning.

By the way..... All 17 of my skis run, flawlessly. Huh, maybe I AM a genius????

[whazguude]

Re: Carburator tuning.

Pretty sure I saw something about Florida having some leftover obama ebt and wic cards. Grab some up, and go get you some fish tacos.

[driftmaster]

Re: Carburator tuning.

Should have left it stock. LOL

What a A$$ hole comment, not surprising by who it came from. Your time would be better spent playing with your Star Wars action figures in your mothers basement.